Do you know the medicines you should never take together?

On the pill? Use cold medicine? Take supplements? These common combinations are actually dangerous.

Photo: iStock

We live in an age where it’s easy to avoid pain, even death, by popping a pill. They may be powerful and convenient, but medicines are also complex, and without considering how they might interact, or if we’re taking too much, too often, we may set ourselves up for side effects with worse symptoms than those we set out to treat.

And it’s not just prescription medications that can negatively interact with each other – over-the-counter supplements and medications can cause some serious problems, too. More than 50 per cent of calls to the National Prescribing Service’s (NPS) Medicines Line (1300 633 424) about complementary medicines are questions about druginteractions. Those that generate the most enquiries are fish oil, vitamin D, calcium, multivitamins, glucosamine and St John’s wort, which is used to treat mild anxiety and depression.

Beware these drug combos

Here’s what the NPS MedicineWise team have to say about these common but dangerous drugcombinations:*

Antidepressants + NSAIDS

A well-known side effect of non-steroidal anti-inflammatory drugs (NSAIDs) is bleeding of the stomach, which is why not everyone is able to use these medicines. This side effect can also occur with some antidepressant medicines, especially those that inhibit the reuptake of serotonin and/or noradrenaline. So if you take these at the same time, your risk of a stomach bleed could rise. Risk factors increase with age, other medications and dosage of NSAIDs. If you take an antidepressant, ask your GP before combining it with other medications.

Warfarin + Aspirin OR Vitamin K

Warfarin is an anticlotting medicine that’s commonly prescribed to anyone at risk of heart attack, stroke or blood clots. Vitamin K works in the opposite way and helps the blood to clot, so it can affect the way warfarin works. If you’re taking this anticoagulant medicine, you must keep the amount of vitamin K in your diet consistent (sources include leafy green veg such as spinach). Aspirin also acts to thin the blood and prevent clotting, so taking it with warfarin may increase the risk of bleeding. Sometimes these medicines are prescribed together, and the combination should only be used on advice from your doctor. Signs of internal bleeding may include unexplained bruising, dark red or brown urine, or dark or black bowel movements.

Blood pressure medicine + potassium

Blood-pressure lowering medicines from the angiotensin converting enzyme inhibitor or angiotensin receptor blocker families may cause more potassium to stay in the body. Taking supplements with one of these medicines could lead to potassium levels in the body being too high. In extreme cases, this could affect the function of the heart. Always check with your doctor or pharmacist before combining any new drugs or supplements with your existing medicines.

Osteoporosis medicine + mineral supplements

Calcium, iron, magnesium and zinc are all minerals that can interact with bisphosphonate, medicines that are used to treat osteoporosis. This can mean less medicine is absorbed, so it’s less effective. Youshould take mineral supplements and osteoporosis medicines at least two hours apart. Most bisphosphonate medicines should be taken at least 30 minutes before food. Check with yourpharmacist about the best instructions for how to take osteoporosis medicine and advise them and your other healthcare professionals about any other medicines you may be taking.

St John's Wort + antidepressants or The Pill

St John’s wort is a complementary medicine that can be helpful in the management of mild or moderate depression. When used with antidepressants, St John’s wort can cause a serious reaction called serotonin syndrome or serotonin toxicity. For this reason, don’t take St John’s wort with other antidepressants. Symptoms of serotonin syndrome include confusion, agitation, restlessness, sweating, tremor, even loss of consciousness and death. It may also reduce the effectiveness of oral contraceptives. If you’re taking St John’s wort, check with your doctor or pharmacist about possible interactions with your other prescription and non-prescription drugs.

Alcohol + sedatives or cold medicine

Alcohol can take several hours to have an effect, so it’s important to understand that interactions don’t only happen when you consume medicines and alcohol at the same time. Alcohol can increase the effect of medicines that relax or sedate the body, such as sleeping tablets, anti-anxiety medicines and antidepressants. Many cough, cold, allergy and travel sickness medicines contain ingredients that relax or sedate the body. These ingredients may interact with alcohol to cause increased drowsiness and dizziness. Common pain drugs such as aspirin, celecoxib, ibuprofen and naproxen, together with moderate amounts of alcohol may increase the risk of stomach irritation. Check with your pharmacist about having alcohol when taking any medicine.

Caffeine + stimulants

Caffeine can increase the effects of some medicines and may not interact well with others. For example, some medicines actually contain caffeine so if youdrink caffeine while taking this medicine, you might end up with too much in your body, which can lead to difficulty sleeping, restlessness and headaches. Caffeine is a stimulant so combining it with medicines that have similar stimulant effects, such as pseudoephedrine or phenylephrine in cold and flu medicines, may increase effects like palpitations or a racing heartbeat, or difficulty sleeping. Caffeine can also interact with phentermine, which is used to suppress appetite, and medicines prescribed for ADHD.

*The advice here isn’t applicable to everyone’s circumstances. Speak to your own pharmacist or doctor to check if combined use is appropriate.

Be extra safe with these tips

Keep an up-to-date medicines list using the NPS MedicineWise app (free for iPhone and Android).

Identify your medicines by their active ingredient rather than brand name.

Properly measure out liquid medication with a calibrated syringe or cup.

Grapefruit: be aware of your risks

The interactions between grapefruit and grapefruit juice with medicines for heart conditions, high blood pressure, high cholesterol, depression, anxiety and sleep problems have been known for some time, but it’s now known to impact on more than 85 medicines.

The interaction affects the way a medicine is broken down in the body, so the amount of medicine from each dose in the body is increased, which may lead to side effects. If you eat grapefruit or drink grapefruit juice and also take a prescription medicine, check with your pharmacist about possible interactions.